Last updated on October 28th, 2023 at 05:40 pm
Q: Have you seen cooking oil catching fire when a frying pan is kept for long on a burning stove?
A: Yes, cooking oil can catch fire if it is heated above its ignition temperature.
Q: Does it mean that ignition temperature of kerosene oil is lower than that of wood?
A: Yes, the ignition temperature of kerosene oil is lower than that of wood.
Q: Why do we need to take special care in storing kerosene oil?
A: We need to take special care in storing kerosene oil because it is a combustible substance and can catch fire easily if not stored properly.
Q: Why does a paper cup not burn when heated with water inside it?
A: The heat supplied to the paper cup is transferred to water by conduction, so the ignition temperature of paper is not reached in the presence of water, and it does not burn.
Q: What are inflammable substances?
A: Inflammable substances are those substances that have a very low ignition temperature and can easily catch fire with a flame. Examples include petrol, alcohol, and Liquefied Petroleum Gas (LPG).
Q: What does a fire brigade do when it arrives at the scene of a fire?
A: A fire brigade pours water on the fire to cool the combustible material so that its temperature is brought below its ignition temperature. This prevents the fire from spreading. Water vapours also surround the combustible material, helping to cut off the supply of air.
Q: What are the three essential requirements for producing fire?
A: The three essential requirements for producing fire are fuel, air (to supply oxygen), and heat (to raise the temperature of the fuel beyond the ignition temperature).
Q: How can fire be controlled?
A: Fire can be controlled by removing one or more of the three essential requirements: fuel, air, or heat. A fire extinguisher is designed to cut off the supply of air, bring down the temperature of the fuel, or both. In some cases, it may not be possible to eliminate all three requirements.
Q: What is rapid combustion?
A: Rapid combustion is a type of combustion in which a fuel burns rapidly, producing heat and light.
Q: What is spontaneous combustion?
A: Spontaneous combustion is a type of combustion in which a material suddenly bursts into flames, without the application of any apparent cause.
Q: What is an explosion?
A: An explosion is a sudden and violent release of energy, heat, light and sound, typically as a result of a chemical reaction or a sudden increase in pressure.
Q: What substances give flames during burning?
A: Substances that vaporize during burning, such as kerosene oil and molten wax, rise through the wick and are vaporized during burning, forming flames.
Q: Can you list some common fuels and group them as solid, liquid and gaseous?
A: Solid fuels: Wood, coal, charcoal, cow dung cakes
Liquid fuels: Petrol, diesel, kerosene, alcohol
Gaseous fuels: LPG, natural gas, biogas
Q: What are the harmful effects of increasing fuel consumption on the environment?
A: Increasing fuel consumption leads to higher emissions of pollutants such as carbon dioxide, carbon monoxide, nitrogen oxides, and fine particles. These pollutants contribute to air pollution, which can cause respiratory diseases and other health problems. Burning fossil fuels also leads to the release of greenhouse gases, which contribute to climate change.
Q: What is carbon monoxide gas and why is it dangerous?
A: Carbon monoxide gas is a colourless, odourless, and tasteless gas. It is produced when fuels like wood, coal, petrol, and diesel are burned incompletely. Carbon monoxide is dangerous because it can displace oxygen in the bloodstream and cause suffocation. It can also cause headaches, dizziness, nausea, and even death.
Q: What is the harmful effect of increased concentration of carbon dioxide in the air?
A: Increased concentration of carbon dioxide in the air is harmful because it leads to global warming. Carbon dioxide is a greenhouse gas that traps heat in the atmosphere and causes the Earth’s temperature to rise. This can lead to a range of environmental problems, including melting of glaciers, rising sea levels, and extreme weather conditions.
Q: What gas is released by burning coal and diesel, and what harmful effects does it have?
A: Burning coal and diesel releases sulphur dioxide gas, which is an extremely suffocating and corrosive gas. It can cause respiratory problems, such as bronchitis and asthma. Sulphur dioxide also contributes to the formation of acid rain, which has harmful effects on crops, buildings, and soil.
Q: What is acid rain and how is it formed?
A: Acid rain is a type of rain that is more acidic than normal rainwater. It is formed when gases like sulphur dioxide and nitrogen oxides dissolve in rainwater and form acids like sulphuric acid and nitric acid. Acid rain can damage crops, buildings, and soil. It can also make lakes and rivers too acidic for aquatic life to survive.
Q: Why is CNG considered a cleaner fuel than diesel and petrol?
A: CNG is considered a cleaner fuel than diesel and petrol because it produces fewer harmful emissions when burned. CNG burns more cleanly than diesel or petrol and produces lower levels of carbon monoxide, sulphur dioxide, and nitrogen oxides. Additionally, CNG is a domestic source of energy, which reduces dependence on foreign oil.
Class 8 Science Combustion and Flame Extra Question Answer
Fill in the blanks:
- Combustion is a chemical process in which a substance reacts with ___________ to give off heat and sometimes light. [OXYGEN]
- The lowest temperature at which a substance catches fire is known as its ___________ temperature.[IGNITION]
- Inflammable substances have a very low ignition temperature and can easily catch fire with a ___________.[FLAME]
- A substance that disrupts the contact between air and fire is called a ___________. [FIRE EXTINGUISHER]
- Water is an effective substance in firefighting because it cools down the fuel below its ___________ temperature.[IGNITION]
- Rapid combustion occurs when combustion takes place rapidly, usually by applying a ___________.[FLAME]
- During the ignition of a substance like a firecracker, a sudden reaction with the release of heat, light, and sound is known as ___________.[EXPLOSION]
- The rate of combustion is affected by the presence of ___________ in the environment.[OXYGEN]
Class 8 Combustion and Flame True/False
- Combustion is a chemical process that releases heat and sometimes light when a substance reacts with oxygen. [TRUE]
- The ignition temperature is the highest temperature at which a substance can catch fire.[FALSE]
- Inflammable substances have a high ignition temperature and are difficult to ignite.[FALSE]
- Water is a suitable extinguisher for electrical fires and fires involving oils.[FALSE]
- Carbon dioxide is heavier than oxygen and can be used to cover and suppress fires.[TRUE]
- Rapid combustion is a slow and controlled burning process.[FALSE]
- Spontaneous combustion is when a material bursts into flames without any apparent cause or external ignition source.[TRUE]
- Explosion is a type of combustion that occurs slowly and without a sudden release of heat, light, and gas.[FALSE]
- The rate of combustion is influenced by the presence of oxygen in the surroundings.[TRUE]
- The primary purpose of a fuel is to create electricity.[FALSE]
Answer in short:
Q: Name a common gaseous fuel used in vehicles.
A: LPG (Liquefied Petroleum Gas).
Q: What is the lowest temperature at which a substance can catch fire called?
A: Ignition temperature.
Q: Give an example of an inflammable substance.
A: Petrol.
Q: What is the primary purpose of a fire extinguisher?
A: To disrupt the contact between air and the fire.
Q: What is the recommended extinguisher for fires involving electrical equipment and inflammable materials like petrol?
A: Carbon dioxide.
Q: Which type of combustion involves a sudden release of heat, light, sound, and gas?
A: Explosion.
Q: What factor affects the rate of combustion by a combustible substance?
A: The presence of oxygen.
| MCQ on Light Class 8 |
| MCQ on Stars and the Solar System Class 8 |
| MCQ on Pollution of Air and Water |
